This invention relates to improvements in a plastic window panel and a process for producing the plastic window panel, by which the plastic window panel can be improved in strength, rigidity and surface hardness and lowered in thermal expansion coefficient without being lowered in light transmittance.
In automotive vehicles, glass (inorganic glass) panel usually occupies a large part of the outer surface of a vehicle body and therefore is an important part from the viewpoints of vehicle driving and external appearance. Glass panel is becoming high in freedom in shape upon appearance of a variety of bent glass panels, and additionally an area to be occupied with glass panel is further increasing. Accordingly, both weight-lightening and safety are required for glass panels to be used in automotive vehicles. In view of this, it has been proposed to use a panel made of organic glass in place of inorganic glass panel. However, organic glass panel is difficult to be applied for a large-size window of an automotive vehicle. In order to tackle this, it has been hitherto proposed to add glass fiber as a reinforcing material to organic glass so as to improve a rigidity of the organic glass panel; however, glass fiber usually has a diameter of about 10 microns and a length of about 200 microns and therefore prevents visible light from passing through the organic glass panel so that the organic glass panel becomes opaque upon reflection of visible light. As a result, securing a field of view is difficult, and therefore such an organic glass panel is not practical from the safety view point.
Besides, organic glass is low in surface hardness as compared inorganic glass, and therefore it tends to be readily scratched upon being scrubbed with a windshield wiper. As a result, organic glass is difficult to be applied to a window panel for an automotive vehicle. In order to tackle this, it has been proposed to accomplish a surface treatment of organic silane compound at the surface of the organic glass panel. However, even with such a surface treatment, the organic glass panel is low in surface hardness, so that the organic glass panel is insufficient in scratch resistance over a long period.
Furthermore, it has been proposed that an inorganic glass is laminated on the surface of the organic glass panel in order to ensure high rigidity and surface hardness. However, such a laminated panel may cause separation between the inorganic glass and the organic glass under the difference in thermal expansion between them. This makes it difficult to ensure the field of view, and therefore such a laminated panel is not practical.
Recently, sputtering silica on a plastic sheet has been carried out in order to harden the surface of and improve the rigidity of the plastic sheet used as a plastic memory disk for an electronic component. However, in this technique, silica atoms are adhered onto the surface of the plastic sheet or base under vacuum, and therefor the technique is not suitable for a large-size part so as to be low in production efficiency.
In addition to the above, a variety of proposals have been made on improvements in and around organic glass as disclosed in Japanese Patent 7-47644, Japanese Patent Provisional Publication No. 5-86241, Japanese Patent Provisional Publication No. 5-194851, Japanese Patent Provisional Publication 5-306370, Japanese Patent Provisional Publication No. 6-41346, Japanese Patent Provisional Publication No. 6-248176, Japanese Patent Provisional Publication No. 7-26123, and an article (pages 144 to 151) and another article (pages 137 to 143) in Japanese technical journal xe2x80x9cTosou-kougaku (Painting Engineering)xe2x80x9d, Vol. 32, No. 4 (1997).
However, any of the above earlier technologies for improving the characteristics of organic glass has not been able to provide a plastic window panel having the characteristics suitable for window panels (such as windshield and the like) of an automotive vehicle.
It is an object of the present invention to provide an improved plastic window panel which can overcome drawbacks encountered in plastic panels produced by earlier technologies.
Another object of the present invention is to provide an improved plastic window panel which is high in strength, rigidity, surface hardness and low in thermal expansion coefficient as compared with a panel of a single transparent resin, without lowering a light transmittance of a transparent high molecular weight polymer (hereinafter xe2x80x9chigh polymerxe2x80x9d) serving as a matrix.
A further object of the present invention is to provide an improved plastic window panel which can be reduced in thickness and therefore become light in weight as compared with a conventional organic glass panel, because the plastic window panel is improved in strength and rigidity.
A still further object of the present invention is to provide an improved plastic window panel which can be high in surface hardness so as to be prevented from being scratched at its surface even upon a long time use as compared with a conventional organic glass panel, because a conventional hard coating formed of organic silane compound has been insufficient in surface hardness.
A still further object of the present invention is to provide an improved plastic window panel which can be low in thermal expansion coefficient so as to be prevented from being unevenly deformed even at a high temperature condition in summer, because the plastic window panel is low in thermal expansion coefficient.
A first aspect of the present invention resides in a plastic window panel which comprises a plastic panel of a transparent noncrystalline organic high polymer; and silica particulate dispersed in the plastic panel and having a particle size not larger than wavelengths of visible light. The plastic window panel is produced by one of a first method and a second method. The first method comprises (a) providing a first solvent in which the silica particulate having the particle size not larger than wavelengths of visible light is dispersed, and a second solvent in which the transparent noncrystalline organic high polymer is dissolved; (b) mixing the first solvent and the second solvent to obtain a resin composition; and (c) molding the resin composition under heating. The second method comprises (a) providing the silica particulate having the particle size not larger than wavelengths of visible light; (b) mixing the silica particulate into the organic high polymer which is in a process of formation of the organic high polymer, to obtain a resin composition; and (c) molding the resin composition under heating.
A second aspect of the present invention resides in a plastic window panel which comprises a transparent plastic panel; and a surface layer formed on a surface of the plastic panel and formed of a transparent noncrystalline organic high polymer and containing silica particulate having a particle size not larger than wavelengths of visible light, the surface layer having a gradation in a silica particulate concentration in which the concentration of the silica particulate gradually lowers toward a center in thickness of the plastic window panel, the surface layer including a surface-most layer having a silica particulate concentration ranging from 50 to 92% by weight. The plastic window panel is produced by one of a first method and a second method. The first method comprises: (a) providing a first solvent in which the silica particulate having the particle size not larger than wavelengths of visible light is dispersed, and a second solvent in which the transparent noncrystalline organic high polymer is dissolved; (b) mixing the first solvent and the second solvent to obtain a resin composition; (c) dissolving the resin composition in a solvent to form a resinous solution; (d) applying the resinous solution onto the plastic panel; and (e) drying he resinous solution on the plastic panel at a temperature ranging from 18 to 25xc2x0 C. and at a drying rate ranging from 16 to 32 kg/M2 so as to form the surface layer. The second method comprises: (a) providing the silica particulate having the particle size not larger than wavelengths of visible light; (b) mixing the silica particulate into the organic high polymer which is in a process of formation of the organic high polymer, to obtain a resin composition; (c) dissolving the resin composition in a solvent to form a resinous solution; (d) applying the resinous solution onto the plastic panel; and (e) drying the resinous solution on the plastic panel at a temperature ranging from 18 to 25xc2x0 C. and at a drying rate ranging from 16 to 32 kg/m2xc2x7hr, so as to form the surface layer.
A third aspect of the present invention resides in a process for producing a plastic window panel, which process is one of a first process and a second process. The first process comprising: (a) providing a first solvent in which silica particulate having a particle size not larger than wavelengths of visible light is dispersed, and a second solvent in which a transparent noncrystalline organic high polymer is dissolved; (b) mixing the first solvent and the second solvent to obtain a resin composition; and (c) molding the resin composition under heating. The second process comprises (a) providing silica particulate having a particle size not larger than wavelengths of visible light; (b) mixing the silica particulate into a transparent noncrystalline organic high polymer which is in a process of formation of the organic high polymer, to obtain a resin composition; and (c) molding the resin composition under heating.
A fourth aspect of the present invention resides in a process for producing a plastic window panel including a transparent plastic panel, and a surface layer formed on a surface of the plastic panel and formed of a transparent noncrystalline organic high polymer and containing silica particulate having a particle size not larger than wavelengths of visible light, the surface layer having a gradation in a silica particulate concentration in which the concentration of the silica particulate gradually lowers toward a center in thickness of the plastic window panel, the surface layer including a surface-most layer having a silica particulate concentration ranging from 50 to 92% by weight. The producing process is one of a first process and a second process. The first process comprises (a) providing a first solvent in which the silica particulate having the particle size not larger than wavelengths of visible light is dispersed, and a second solvent in which the transparent noncrystalline organic high polymer is dissolved; (b) mixing the first solvent and the second solvent to obtain a resin composition having a ratio in % by weight between the silica particulate and the organic high polymer being 41/59 to 79/21; (c) dissolving the resin composition in a solvent to form a resinous solution; (d) applying the resinous solution onto the plastic panel; and (e) drying the resinous solution on the plastic panel at a temperature ranging from 18 to 25xc2x0 C. and at a drying rate ranging from 16 to 32 kg/m2 so as to form the surface layer. The second process comprises (a) providing the silica particulate having the particle size not larger than wavelengths of visible light; (b) mixing the silica particulate into the organic high polymer which is in a process of formation of the organic high polymer, to obtain a resin composition; (c) dissolving the resin composition in a solvent to form a resinous solution; (d) applying the resinous solution onto the transparent plastic panel; and (e) drying the resinous solution on the transparent plastic panel at a temperature ranging from 18 to 25xc2x0 C. and at a drying rate ranging from 16 to 32 kg/m2, so as to form the surface layer.